The Seaside Sparrow is a habitat specialist of salt and brackish marshes. First described by Wilson 1811, it has attracted the interest of systematists since the end of the 19th century. Occurring in relatively small, localized populations along the Atlantic and Gulf coasts of the United States, this species has been divided into several morphologically distinct subspecies.
This sparrow is socially monogamous although extrapair matings have been reported from South Carolina. Although territorial, it often feeds long distances from the defended space around its nest, a response to wide separation of nesting and feeding areas in the tidal zones it inhabits. Under ideal conditions, it may occur at high population densities, a reflection of the high productivity of salt marshes. Optimal habitat is found in marshes with expanses of medium-high cordgrass with a turf of clumped, residual stems. Especially suitable are spots not subject to extreme flooding that have open muddy areas for feeding. Nest mortality of northern populations is caused mainly by storm flooding; flooding is a significant mortality factor among southern groups, but predation is also important, and its intensity is often related to changes in water levels.
As a maritime wetland specialist, the Seaside Sparrow represents a potentially valuable “indicator” of continued ecological integrity of certain types of coastal marshes and has already proven sensitive to habitat modification in Florida. The melanistic Dusky Seaside Sparrow (A. m. nigrescens) of east-central Florida is extinct; the pale Cape Sable Seaside Sparrow (A. m. mirabilis) of the Florida Everglades is endangered. Other populations are as likely to be susceptible to habitat disturbance and restriction as those in Florida. The species has been studied in detail in the Northeast (Woolfenden 1956a, Post et al. 1983) and Florida (Post et al. 1983, Werner and Woolfenden 1983, Lockwood et al. 1997)